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THIS SNOWPACK SUMMARY EXPIRED ON December 23, 2014 @ 9:10 amSnowpack Summary published on December 22, 2014 @ 4:10 pm

Issued by
Ben Bernall - Kootenai National Forest

Avalanche Character 1: Storm Slab

Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

The surface soft slab fails with easy force (wrist taps) on the buried surface hoar layer and propagates across the extended column. This soft slab over time with additional storm loading could develop into a persistent slab atop the 2 inch buried surface hoar layer. Currently boot penetration through this slab is very common and collapsing of this layer is common above 5500 feet.

Avalanche Character 2: Wind Slab

Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

In my travels today, I ventured out onto several wind loaded slopes. Here I found a 3-4 inch hard wind slab that was very cohesive over topping the storm slab described above. The wind slab was easily penetrated with boots but supported a snowmobile. It would be adviseable to avoid these wind slabs on lee slopes and where cross loading occured.

Snowpack Discussion

The past weekend storms added complexity to our snowpack. Weather forecasts lead us to believe that avalanche hazard will increase through Wednesday. With storm loading and wind transport in the forecast, back country travelers need to be proficient at identifying wind loaded slopes and avoid these, especially at higher elevations. We recommend conservative terrain choices above 6000 feet. Evaluate snowpack and terrain carefully, and please continue to use proven safe crossing procedures and exercise good decision making. HAPPY HOLIDAYS and be safe out there!

Today I visited Chicago Peak (7018 feet) in the East Cabinet Range. Enroute to my pit site I experienced collapsing. On a moderate southwest aspect protected from the wind, I found 37 inches of total snow. The top 6 inches was very soft new snow from the last 36 hours. Below that was 7 inches of 4 finger soft slab snow sitting atop a 2 inch layer of very soft snow containing buried surface hoar (2-4 mm size)

(blue card and pit brush frame the buried surface hoar layer).

Below these surface soft layers is the November benchmark rain crust layer of 9 inches. Below the rain crust is another 9 inches of 1 finger hard slab snow and the bottom 4 inches is loosely consolidated basal snow.

The layer of surface hoar above the crust was able to propagate fractures with easy force in our Extended Column Tests.

The remaining 22 inches of the snowpack is very cohesive and fails near the ground line with hard force in stability tests.

weather

Weather since the Friday advisory has been warm and wet at all SNOTEL sites. Daytime temperatures were above freezing to the mid 30s F. Night time temperatures were below freezing to the upper 20s F. SWE increases were 0.4 to 2.0 inches and nearly all came in the form of snow. New snowfall ranged from 4 to 10 inches with the West Cabinet Range showing the most. Today's weather at Chicago Peak (7018 feet) was mountain fog above 6000 feet, 25º F, west winds 3-5 mph, and 3 inches of new snow overnight

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.